While mass shootings will continue to occur, reducing the access to semi-auto, external box fed magazine fed firearms will reduce the rounds per minute that mass shooters can achieve, thus lowering the casualty count.

The rounds per minute that semi-auto, external box magazine fed firearms can achieve is excessive and makes them weapons of war over being tools.

In a high-stress self-defense situation the ability to fire multiple rounds in quick succession is vital in countering the loss of accuracy incurred under stress. If you have only a bolt action/lever/pump, you might as well have a single-shot musket for all the good one round will do you.

Using a clip it's possible to reload a weapon with an internal magazine nearly as fast as inserting an external magazine. It all depends on how the access to the internal magazine is designed.

If you outlaw guns, only outlaws will have guns. Meaning mass shooters will still be able to get semi-auto, external box magazine fed firearms if they try hard enough.

Rate of fire and reload times are highly negligible considering police response times.

Such a ban would miss the point.

This violates the Second Amendment, stating "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

It is fairly easy to build your own semi-automatic rifles.

Semi-automatic rifles are owned and used more often for legal purposes than for crime. Therefore banning them will obviously have an overwhelmingly negative impact on the tens of millions of people who own them legally compared to the non-existent effect on the several hundred people who use them illegally per year.